RAJASTHAN ­ PET Rajasthan PET Solved Paper-2006

  • question_answer
    If\[2\left[ \frac{1}{2n+1}+\frac{1}{3{{(2n+1)}^{3}}}+\frac{1}{5{{(2n+1)}^{5}}}+... \right]\]\[=\log \left( \frac{n+1}{n} \right),\]then the value of n for which equation will satisfied, is

    A)  for \[-1<n<0\]     

    B)  for\[n>-1\]or\[n<0\]

    C)  for all\[n\ne 0,-1\]    

    D)  for no value of n

    Correct Answer: B

    Solution :

     Given, \[2\left[ \frac{1}{2n+1}+\frac{1}{3{{(2n+1)}^{3}}}+.... \right]=\log \left( \frac{n+1}{n} \right)\] \[-1<\frac{1}{2n+1}<1\] Now, \[-1<\frac{1}{2n+1}\]or\[\frac{1}{2n+1}<1\] \[\Rightarrow \] \[-(2n+1)<1\]or\[1<2n+1\] \[\Rightarrow \] \[-2n<2\]or\[0<2n\] \[\Rightarrow \] \[-n<1\]or\[0<n\] \[\Rightarrow \] \[n>-1\]or\[0<n\]


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